As someone who thought Archer's legendary seemed "Meh" (though, to be fair, I believe what I actually said was "Archer's seems meh unless they give her the mistress treatment" ... and that's exactly what they did), I don't want to pass judgement too quickly on any of these.
Sure, Mega's longevity is an issue, but there are some fights that last the full 90 seconds. I timeout in Coli all the time.
Remember that we don't know what the scaling will be on all of these skills. If Mega gains 9,001 dmg every second, that would still be pretty good because 5 seconds in he would have 45,005 dmg, right?
Genie's str buff might be similarly high; his ability to remove an enemy from the fight for 3 seconds sounds really good, too, especially since it cannot be stopped. You will essentially be fighting 5v4 for 75% of the fight!
Anyway, here's my hottake -
Witch - seems kind of meh, to be honest. Unless the amount of reduced dodge/attack is pretty high, her orange just seems like an added bonus to using her (which I do very often already) as opposed to a reason to user her when I might otherwise not.
Trio - I don't understand the wording. Do they combine after doing their white now? Will that actually make them do less damage? Idk.
Genie - how much will the str buff be? The second part seems decent. Not sure it moves the needle for me, but it might play better than it reads.
Mega - how much will he gain? The current meta is brutal on tanks, and I can't see this working out very well for him. But hey, maybe it's the Archer treatment!
Spikey - sounds interesting! I have concerns that shields will either be gone or the fight will be over before he whites (at least that's how most battles play out in FP right now, it seems). I like Nigh Quill's energy drain, but will it be tied to doing damage? If so, might not help much against Horse lines, but other lines would be great!
Corgi - seems pretty good, I guess? Heavy foes off the top of my head - Kaiju, Archer, Cyclops, Ninja, bunch of tanks, Spider ... so less damage from Archer and Kaiju is nice. Will be interested to see how useful the second part is. I will also be curious to see if "undamaged" includes shielded foes. If you use "Grab that Tail" against a Horse Bro line and do 0 damage to anyone ... are they all converted? What happens then, do you just win? Actually, what happens if you use Grab that Tail while only 2 heroes are alive - it hits 1 hero, killing them, and converts the other. Do you win that? Is conversion like Spectral's possession?
Overall, I like them. They sound interesting.